Non-Ising polar domain walls have recently emerged as individual two-dimensional materials exhibiting localized nonlinear optical emission. The analysis of this emitted light often requires focusing with high apertures. As a result, the vectorial properties of light come into play. This study provides an analytic treatment of the vector light fields’ effect on the polarized second-harmonic emission (SHG) arising at polar domain walls. While confined optical fields are expected to alter the SHG polarization response, we identify extrinsic and intrinsic properties capable of canceling focusing effects. We determine a precise combination of the fundamental wave polarization and orientation of the domain walls at which focusing effects are negligible. Furthermore, the perimeter defined by the domain walls intrinsic optical parameters below which focusing effects are negligible is extracted from a systematic focus-dependent analysis. Our study provides the necessary methodology and precautions to probe the internal structure of non-Ising domain walls with confined optical fields, and it can be extended to explore newly discovered ferroelectric topologic nanostructures.

中文翻译：

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非伊辛极畴壁上极化二次谐波发射的聚焦特性

非伊辛极性畴壁最近作为呈现局部非线性光发射的单个二维材料出现。对这种发射光的分析通常需要使用大光圈聚焦。因此，光的矢量特性开始发挥作用。这项研究提供了矢量光场对极化二次谐波发射 (SHG) 产生于极畴壁的影响的分析处理。虽然预计受限光场会改变 SHG 偏振响应，但我们确定了能够消除聚焦效应的外在和内在特性。我们确定了基波极化和畴壁方向的精确组合，其中聚焦效应可以忽略不计。此外，从系统的焦点相关分析中提取由畴壁固有光学参数定义的周长，低于该参数时聚焦效应可以忽略不计。我们的研究为探测具有受限光场的非伊辛畴壁的内部结构提供了必要的方法和预防措施，并且可以扩展到探索新发现的铁电拓扑纳米结构。